A laboratory study of flow characteristics in natural heterogeneous vegetation patches under submerged conditions

Abstract

Existing studies on flow through vegetation have focused mainly on understanding the turbulent structure in vegetated channels of single plant type. However, in natural riverine environments, vegetation also occurs as patches with heterogeneous plant forms. The present paper investigates the flow and turbulent characteristics in heterogeneous vegetation patches at a laboratory scale. Experiments were conducted using different forms (grass, leafy and cylindrical) of natural vegetation planted, alternatively and also as a mixed variety of patches in a staggered pattern. The results show that the presence of other vegetation forms in mixed heterogeneous patch increases the velocity reduction up to 10% compared to flexible grass. Moreover, additional drag due to mixed vegetation reduces shear generated turbulence at the canopy top and shifts its peak above the canopy. In the case of heterogeneous patches, spatial heterogeneity in velocity fields and, varying zones of increased and diminished turbulence were observed. Specifically, patch form and its alignment significantly control the velocity reduction and, momentum transfer between the canopy and overflow regions. These findings and furthermore studies on heterogeneous patches may be helpful for riparian management practices in creating ecological and sediment deposition zones.